Physics Radiation: Shields up Unless astronauts can be protected from exposure to dangerous levels of radiation it might mean there will only ever be one way tickets to Mars. In this lesson you will investigate the following: • What is radiation? • When is radiation dangerous? • If radiation causes cancer how can it be used to treat cancer? Let’s see if a new protective shield will deflect the cosmic attacks. This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com Introduction: Radiation In space it’s the stuff you can’t see that can kill you! A vacuum that would make your eyes pop out and a temperature cold enough to freeze air are obvious dangers, but just as deadly is the invisible stream of cosmic radiation that could kill you even if you never went outside your spacecraft. High-energy charged particles are beamed out when stars explode, hurtling across the cosmos and tearing through anything in their path, including the bodies of astronauts. Then there are the less energetic particles that stream from the Sun – still powerful enough to present a serious cancer risk. Scientists are thinking about how we can protect astronauts from these rays as they travel to Mars, a trip that will take more than two years. They've come up with the Space Radiation Superconductive Shield (SR2S) – a giant magnetic shield designed to wrap around spacecraft and deflect cosmic rays much like the Earth's magnetic field protects the planet. It’s a great idea, but there’s one problem. Such a shield would use so much energy that there wouldn’t be enough left to power other vital operations on the spacecraft, like temperature control and air circulation. So the scientists are experimenting with superconductors that allow electrical current – electrons – to flow freely. So freely that they don’t use any energy at all. The shields can be charged by the Sun and stay charged for years. Oh, and superconductors only work at very low temperatures. But that’s no problem in space, where the temperature is -263° C. So, shields up, ready for Mars! Read or listen to the full Cosmos magazine article here. Geiger counters are used to check for radiation leaks from drums of radioactive material. Question 1 Identify: What does radiation make you think of? Use the mind map below to show everything you know about radiation or that you've heard about it. Sub Idea... Sub Idea... Radiation Sub Idea... Sub Idea... For best results when printing activities, enable your web browser to print background colours and images. Gather: Radiation What is radiation? Radiation at work – from left, an infrared thermal imaging device showing heat loss from a building; a microwave oven; a radio telescope in New Mexico, USA; and a 3D X-ray of a hand. 0:00 Question 1 Define: What is radiation? Question 2 Complete: Use information from the video to fill in the table below, explaining the helpful roles of some types of wave radiation. Also, indicate whether each type of radiation is ionizing or non-ionizing. Type of electromagnetic Is useful for... Ionizing or non-ionizing radiation Visible light Infrared radiation Microwaves Radio waves Ultraviolet radiation Not applicable X-rays Gamma rays Not applicable Question 3 Question 4 Select: Ionizing radiation: Recall: Beta particles are: can be particles or waves. less ionizing than both alpha particles and gamma rays. transfers energy to atoms that it strikes. more ionizing than both alpha particles and removes electrons from atoms that it strikes. gamma rays. All of the above. more ionizing than alpha particles and less ionizing than gamma rays. Waves Radiation can consist of waves or particles. Stars, including our Sun, emit both. Wave radiation, commonly known as electromagnetic (EM) radiation, includes visible light and radiation from numerous artificial sources such as electric power cables, cooking devices, televisions, radios and mobile phones. Different types of EM radiation carry different amounts of energy. Those with high energy, such as X-rays and gamma rays, are ionizing and so are dangerous to humans. The key things to remember are that EM waves: have no mass, have no electric charge, travel at the speed of light in a vacuum, and may be either ionizing or non-ionizing depending on their energy. Question 5 Interpret: Use the diagram above to help fill in the missing words in the sentences below. Type them into the right hand column. X-rays have shorter wavelengths and ____________ energy than UV radiation. Radio waves have ____________ wavelengths and ____________ energy than gamma rays. Microwaves have ____________ wavelengths and ____________ energy than visible light. EM waves with shorter wavelengths have ____________ energy than EM waves with longer wavelengths. Particles Particle radiation consists of various high-speed subatomic particles. They can be individual particles or, as in the case of alpha radiation, small groups of particles stuck together. They all have mass, although this can be very small. For example the electrons that make up beta radiation have very little mass. Particle radiation includes cosmic rays from outer space – mostly high-energy protons. On Earth we are most familiar with positively charged alpha particles and negatively charged beta particles. Both come from naturally occurring minerals – for example alpha particles are emitted by uranium and beta particles by strontium. The key things to remember are that radiation particles: have mass, can have positive or negative electric charges, or can be electrically neutral, travel at high speeds less than the speed of light, and are ionizing. Question 6 Match: Using information you have learnt from the lesson so far: label boxes describing or showing alpha particles with an "a", and label boxes describing or showing beta particles with a "b". Ionizing radiation Question 7 Identify: The graphic above shows a radiation source producing three different types of ionizing radiation: alpha particles, beta particles and gamma waves. The radiation beams are directed through electrically charged plates before being detected. Identify each type of ionizing radiation and explain your choice. Radiation Type of ionizing Explanation beam radiation A B C Process: Radiation Radiation in space 0:00 0:00 Question 1 Question 2 Remember: Galactic cosmic rays cause tremendous damage to Recollect: Which of the following bodily organs or systems can human cells. Which of the following are reasons for this? be affected by ionizing radiation? Galactic cosmic rays have high velocity Nervous system Genitals Galactic cosmic rays have no mass Eyes Galactic cosmic rays have negative electric charge Glands Galactic cosmic rays have positive electric charge Gastrointestinal system Galactic cosmic rays have high mass Question 3 Question 4 Calculate: In a round trip to Mars, how much more radiation Recall: The Earth is protected from most radiation coming from would astronauts be exposed to compared to an average CT the Sun and other stars just by the ozone layer in its scan? atmosphere. about 70 times more True about 700 times more False about 7 times more Question 5 Consider: Why do you think galactic cosmic rays can cause so many different types of illness in humans? Good radiation, bad radiation When high-energy radiation ionizes atoms it often also destroys the molecules those atoms make up, like DNA. The body can repair low levels of this damage but at higher levels there are two possible outcomes: 1. Short-term high-level exposure can cause irreparable cell damage – enough to kill cells within 24 hours. Called radiation poisoning, this sort of damage often causes death. 2. Long-term lower-level exposure can destabilize DNA molecules without killing cells, but the cells become cancerous, replicating out of control. Radiation causes cancer in most parts of the body but whole-body exposure is most often linked with leukaemia – cancer of the bone marrow. In spite of these effects, high doses of X-rays, gamma rays or particle radiation are used by doctors to cure cancer. They direct the radiation at cancerous cells to kill them. This is called radiation therapy, or radiotherapy. More than 50 per cent of people with cancer undergo radiotherapy as part of their treatment. Ionizing radiation, good and bad. Radioactive spills at nuclear power plants are very dangerous and must be contained as soon as possible. However ionizing radiation is also used to treat cancer, as in the photo at right. Question 6 Calculate: When radiotherapy is prescribed it is very important that the radiation is accurately targeted to the correct area and that an appropriate dose is delivered. This is called the absorbed dose (D), calculated as follows: E D = m where: E is the energy of the radiation, expressed in joules (J), and m is the mass of body tissue irradiated, in kilograms (kg). D, therefore, is measured in joules per kilogram (J/kg). Calculate: i) the absorbed dose received by a 150 g tumour irradiated with 12 J of gamma-ray energy. ii) the absorbed dose received by an 8 g tumour irradiated with 0.25 J of gamma-ray energy. Hint: don't forget the units! Did you know? The typical gamma-ray radiation dose required to treat a solid skin tumour ranges from 60 to 80 J/kg, whereas lymphomas – tumours formed from cancerous white blood cells blocked in the lymph nodes – are treated with 20 to 40 J/kg. This big difference is related to the ratio of mature to immature cells in the different types of tissue, how often the cells replicate, and how long replication takes. Question 7 Speculate: Before patients start radiotherapy a team of specialists discuss the best way to treat their cancer.